a. Field of the Invention
The present disclosure relates to a device for reducing the axial shortening due to repeated deflection of a catheter or catheter access device, such as an access sheath or introducer.
b. Background Art
Many medical procedures require the introduction of specialized medical devices into and/or around the human heart. In particular, there are a number of medical procedures that require the introduction of specialized devices including, but not limited to, catheters, dilators, and needles to areas, such as into the atria or ventricles to access the inner surface of the heart, or into the pericardial sac surrounding the heart to access the epicardial or outer surface of the heart. Catheters and access sheaths or introducers have been used for medical procedures for a number of years. It is typically necessary for introducers and catheters to exhibit a degree of flexibility to be able to maneuver through the vasculature of a patient during the performance of medical procedures. Accordingly, catheters and access sheaths often have deflectable sections located at the distal end portion thereof.
To facilitate deflection, conventional sheaths, introducers, and catheters are commonly configured with steering or pull wires to control the movement and relative curvature of the devices, particularly at the distal end portion. The pull wires typically extend along the length of the catheter or sheath and are coupled and/or connected to a control mechanism at the proximal end portion, such as, for example, a knob that can be rotated or to a robotic control system. In operation, the pull wires are used to “pull” on one side or the other side of the device to control deflection, for example, to deflect the distal end portion. These devices are conventionally made from PEBAX that must withstand the force applied to the pull wire so that the distal end portion bends.
After repeated deflections, however, the deflectable distal end becomes shortened in axial length (i.e., in a state of being compressed relative to the original axial length), particularly after the catheter or access sheath has been resident in the body for some time and is thus at or near body temperature. As a result of the reduced axial length, the catheter or sheath's access capabilities are reduced. An accomplished physical can make some manual adjustments to compensate for the “compressed” distal end (i.e., the loss of travel) but only up to a certain point beyond which the amount the distal end has been shortened is deemed excessive.
To better understand this phenomena, one may notice that in a conventional deflectable access sheath, the inner and outer diameters of the sheath wall may differ by as much as 0.50 inches (e.g., if one considers a 13 Fr. Device with a small curl of 180 degrees). This difference must be accommodated during deflections, which results in a series of compressions and extensions of the polymer material, resulting in the permanent axial shortening or compression described above. Moreover, as the number of deflections increase, the polymer material weakens (as does the braid, usually a part of the construction), begins to give way and eventually may fail. This failure is usually not catastrophic since as described above, a physician can recognize the reduction in available travel in the distal tip section and make adjustments. However, there are situations where the loss of travel may prevent particular areas of the anatomy from being accessed, such as the right superior pulmonary vein (RSPV) and right inferior pulmonary vein (RIPV).
In addition, recent advances in the robotic control of catheters, access sheaths and the like allow advancement, retraction and various deflections and/or steering to be controlled robotically. When the actuation mechanism to “pull” the pull wires is a robotic control system, the physician's ability to compensate for axial shortening described above is inapplicable. And while closed loop feedback systems may be configured to account for the loss of distal travel (i.e., to mimic what a physician would do), it is nonetheless desirable to minimize or eliminate the axial shortening of the deflectable distal end portion in order to provide sufficient control authority to the actuation mechanism as an initial matter.
It is known to include a wire mesh in an introducer catheter, as seen by reference to U.S. Patent Publication 2009/0024110 entitled CATHETER AND INTRODUCER CATHETER HAVING TORQUE TRANSFER LAYER AND METHOD OF MANUFACTURE to Heideman et al (“Heideman”), owned by the common assignee of the present invention, and hereby incorporated by reference in its entirety. Heideman disclose a torque transfer layer in the catheter, which includes a wire mesh, to provide increased strength, flexibility, and kink resistance. While the torque transfer layer provides an excellent platform to improve torque along a shaft, there is still a need for a mechanism to reduce or eliminate axial shortening of a catheter or sheath.
There is therefore a need to minimize or eliminate one or more of the problems as set forth above.